Gully

Soil erosion in the South-eastern part of Nigeria has been identified as the most threatened environmental hazards in the country. Secondary data on the study traced its origin to some 30 years ago when development began to creep into the region, following Nigeria's oil boom of the 1970s. Dugout pits, created from soil excavation activities, for foundation filling and sand for brick making and plastering of buildings produced deep craters and gullies due to perennial erosion from torrential tropical rains. This was further worsened by poor geologic set up of soil found in the area. This, happening over years, and not well managed had resulted to gullies, found in more than 1000 sites with over 700 of them located in Anambra State alone. Its effects spread over five states namely Anambra, Abia, Imo, Enugu and Ebonyi States. This initiated the zoning of the study area into five. Thirty settlements where gullies were mostly pronounced as revealed in previous literature on

During the past decades, land use change in the Lake Victoria basin has significantly increased the sediment fluxes to the lake. These sediments as well as their associated nutrients and pollutants affect the food and water security of millions of people in one of Africa's most densely populated regions. Adequate catchment management strategies, based on a thorough understanding of the factors controlling runoff and sediment discharge are therefore crucial. Nonetheless, studies on the magnitude and dynamics of runoff and sediment discharge are very scarce for the Lake Victoria basin and the African Rift region. We therefore conducted runoff discharge and sediment export measurements in the Upper Rwizi, a catchment in Southwest Uganda, which is representative for the Lake Victoria basin. Land use in this catchment is characterized by grazing area on the high plateaus, banana cropping on the slopes and Cyperus papyrus L. wetlands in the valley bottoms. Due to an increasing population pressure, these papyrus wetlands are currently encroached and transformed into pasture and cropland. Seven subcatchments (358 km2-2120 km2), with different degrees of wetland encroachment, were monitored during the hydrological year June 2009-May 2010. Our results indicate that, due to their strong buffering capacity, papyrus wetlands have a first-order control on runoff and sediment discharge. Subcatchments with intact wetlands have a slower rainfall-runoff response, smaller peak runoff discharges, lower rainfall-runoff ratios and significantly smaller suspended sediment concentrations. This is also reflected in the measured annual area-specific suspended sediment yields (SYs): subcatchments with encroached papyrus swamps have SY values that are about three times larger compared to catchments with intact papyrus vegetation (respectively 106-137 ton km(-2) y(-1) versus 34-37 ton km(-2) y(-1)). We therefore argue that protecting and (where possible) rehabilitating these papyrus wetlands should be a corner stone of catchment management strategies in the Lake Victoria basin.

Soil erosion in the South-eastern part of Nigeria has been identified as the most threatened environmental hazards in the country. Secondary data on the study traced its origin to some 30 years ago when development began to creep into the region, following Nigeria's oil boom of the 1970s. Dugout pits, created from soil excavation activities, for foundation filling and sand for brick making and plastering of buildings produced deep craters and gullies due to perennial erosion from torrential tropical rains. This was further worsened by poor geologic set up of soil found in the area. This, happening over years, and not well managed had resulted to gullies, found in more than 1000 sites with over 700 of them located in Anambra State alone. Its effects spread over five states namely Anambra, Abia, Imo, Enugu and Ebonyi States. This initiated the zoning of the study area into five. Thirty settlements where gullies were mostly pronounced as revealed in previous literature on